In a recent discussion with colleagues, the issue of the precise meaning of the word "should" in a specific context arose. I maintained that when used in a directive (in this case a supplement to the International Maritime Dangerous Goods Code), the term "should" has imperative force.
As one example of many:
"Before handling a CTU, the handling staff should ensure that the lifting equipment is safely and securely attached to it..."
In my opinion, the above is not a recommendation to be ignored at will. Laden 40-foot containers are not something to be toyed with.
The precise legal force of the supplement is unclear, although insurance claims have been decided on the basis of non-adherance to the guidelines.
During translation of a related document into German, the issue arose as to whether to translate the many occurrences of "should" in the form above with a word meaning "must" or with a word meaning "ought to".
Conversely, the issue arose as to whether "should" is an acceptable translation of the German word for "must".
The problem was ultimately solved relatively simply in this specific case insofar as the official English version of the supplement uses "should" consistently and the official German version uses the equivalent of "must", and we followed this line.
The issue has, however, continued to bug me. Merriam-Webster lists the imperative meaning as archaic, whereas OED does not and states "In commands and instructions, equivalent to imperative".
Etymologically, the word clearly has or had imperative force. My question, however (I do have one), is whether real speakers in the real world would understand instructions in this form as having imperative force.
Phil W. 11 November, 2004

In my view, since I assume that there really was no doubt that following the International Maritime Dangerous Goods Code instructions is mandatory rather than discretionary for those affected, you did the right thing.

Similarly, I seem to recall reading a few years ago that the Australian Government has now banned the use of 'shall' in the drafting of its legislation in order to avoid precisely this kind of ambiguity.

Whether real speakers in the real world would understand instructions couched in 'should' terms as having imperative force will probably depend partly on the context in which 'should' is being used, and partly on the linguistic habits of the speech community that is having to interpret the instructions in question.

I feel that where an instruction is mandatory, 'must' is far preferable, especially when it can be assumed that it will also be applicable to, or have to be processed by, non-native readers of English. If something is optional, it should be unambiguously marked by formulations like "If desired, an operator may [perform a given action]".

In non-literary translation, clarity and the avoidance of culturally-dependent interpretation of context is key.

Clearly, unambiguous statements are infinitely preferable, and the remainder of the IMDG Code actually uses the imperative form most of the time. The issue here arose because the English version of the supplement used "should", as did the related documents we were working on and I argued that the meaning was clearly imperative. Other skilled native speakers argued that it was recommendatory. This was where the primary problem lay. Did the authors intend the one or the other reading or did they deliberately obfuscate the issue? And this remains my question, namely how would people actually understand it?
The target audience of the "guidelines" (as they are called) is dockers/longshoremen, or at least the supervisory staff, so we can't necessarily expect to play with linguistic niceties. It is a weakness in the original document, but we felt constrained to opt for one reading or the other.
To confuse the issue still further, the IMDG Code itself is, in my understanding, legally binding in many countries, but some of the supplements primarily provide advice and recommendations (which are nevertheless taken into account in legal decisions).
Fortunately, the project we were translating was merely referencing the supplement. I am rather glad we were not translating the beast itself.

Phil, It’s my feeling that ‘should’ does not generally carry the force of ‘must’ (however, it may with the help of surrounding words – see below). For example, if one said that the speed limit (which in practice really isn’t a limit) of 75 mph on Colorado interstate highways ‘should’ be obeyed. This strikes me as more of a suggestion that one ‘ought to,’ rather than a command to do so. However, in checking through a few dictionaries I found that the definition appears to be somewhat muddled:

Random House Unabridged seems to be saying that it means both MUST and OUGHT: “must; ought (used to indicate duty, propriety, or expediency): ‘You should not do that.’”
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Merriam-Webster’s Unabridged never specifically says ‘must’ in any of its 6 definitions, but it does use the word ‘necessity,’ which, as far as I’m concerned, means an ‘imperative’ requirement and thus would seem to have the same force as ‘must.’ However, the only one-word synonym that they offer in their lengthy discussion is ‘ought.’:

2) Used in auxiliary function to express duty, obligation, NECESSITY, propriety, or expediency <“for 'tis commanded I should do so”— Shakespeare> <”but now he is dead, why should I fast”>— 2 Samuel 12:23 (Revised Standard Version)> <“the law was then passed . . . that every senator should take an oath”— J.A.Froude> <“in such cases the officer should first give notice to those in the house”—Paul Wilson> <“and this is as it should be”— H.L.Savage> <”was determined that his son should have a good education”> <“you should brush your teeth after each meal”>

The ‘Shakespeare’ and the ‘senator’ quotes by force of the surrounding words appear to me to be imperatives.

5) Used in auxiliary function to express what is probable or expected <“this year's treasury deficit should be $6 billion or more”— T.R.Ybarra> <effects of the trends cited above should not be felt . . . for another decade”— A.W.Griswold> <it should be child's play for the three of us”—John Buchan> <recordings which should confuse even the most ingenuous listener”— Robert Evett> <“with an early start, they should be here by noon”>
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The OED discusses ‘should’ under ‘shall’ and tells us that the imperative ‘shall’ is obsolete: “This conditional form of expression was from an early period substituted for the unconditional ‘shall’ in sense 2, and in modern English the present tense in this use is obsolete, and SHOULD = OUGHT TO.”
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The American Heritage Dictionary lists the imperative (under ‘shall’) as archaic: “2) Archaic. a) To be able to. b) to have to; must”
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So my vote is that ‘should’ is not an imperative, unless some surrounding words force it into being so. And I would certainly be very wary about using ‘should’ for ‘must’ in any legal document.
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Ken,
As I said, the problem was not so much using "should" for "must" (although I also posed that question above), but how to interpret "should" as it stood in the original.
It is the online M-W that lists the "must" meaning as archaic.
You suggest that "the surrounding words" force "should" to have an imperative meaning and Erik suggests more broadly that the context dictates the meaning, and undoubtedly you are both right.
I seem to remember my old school uniform code saying something along the lines of "trousers should be grey flannel". I was sent home for turning up in purple bell-bottoms (now guess my age!). Alternatively, the school announcement "all those caught smoking yesterday should report to the headmaster at 9 o'clock prompt" - also an imperative instruction which affected me.
In context, I would still maintain that the instructions in the supplement to the IMDG code had imperative meaning, irrespective of the actual legal force of the document.
If you choose to comply with the guidelines, the recommendations are to be taken at face value, but you can choose (at your peril) not to observe them in your operation.

Dale, ????? The button above the right column says ‘writing or usage queries’ and the one above the left column says ‘word or phrase origins.’ This is the right column. The ‘should’ question was one of usage and not origin. I think you should be able to take it from there. If you have any further questions . . . . you’re in serious trouble! (<;)

Ken, that's why I say you must write a guide to the uninitiated. There must be several of us. For instance, don't "gerund and infinitive..." and "panned by the critics" belong under "usage:? "dissemble" under "origin"?
Let's get after 'em all, grind 'em into the tarmac

Dale,
Imagine I wanted to drive a (tapered) stake through your heart - not that I would want to, but just imagine. I'm imagining it now. Would the way it tapers depend on whether I started from your chest or your back?